Prepare the peppers:
Preheat your oven to 375°F (190°C). Cut the tops off the bell peppers and remove the seeds and membranes. Rub the outside of the peppers with 1 tablespoon of sunflower oil and place them in a baking dish.

Prepare the filling:
In a large skillet, heat the remaining 1 tablespoon of sunflower oil over medium heat. Add the ground beef and cook until browned, breaking it up into small pieces with a spoon. Drain excess fat if needed.

Add vegetables:
Stir in the chopped onion and garlic, cooking until softened. Add the diced tomato, carrots, zucchini, and mushrooms.
Cook for about 5-7 minutes until the vegetables are tender.

Season:
Season the mixture with dried oregano, dried basil, salt, and pepper to taste. Stir in the cooked rice until well combined.

Stuff the peppers:
Spoon the beef and rice mixture evenly into the prepared bell peppers, pressing down gently to pack the filling.

Bake:
Cover the baking dish with foil and bake in the preheated oven for 30-35 minutes, or until the peppers are tender.

Optional cheese topping:
If desired, uncover the peppers, sprinkle shredded mozzarella cheese over the tops, and bake for an additional 5 minutes or until the cheese is melted and bubbly.

Serve:
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley or basil before serving.